The green represents Native American land, and any part that turns white was ceded. She writes: "Made because I was having trouble visualizing the sheer scale of the land loss, and reading numbers like 'blah blah million acres' wasn’t really doing it for me." Numbers wise, the amount of green land shown after 1895 is about 2.3 percent of the original size.
The animated gif was created by sunisup and posted to her tumblr account.
Two things came to mind after seeing this image: 1) Not only does this map illustrate the loss of land it also illustrates the mass murder of a diverse group of cultures; 2)I'd like to see a similar image of Canada.
There is no doubt that current inhabitants of North America are living on occupied land and it would best if we all kept that in mind when we start feeling all warm and fuzzy and patriotic.